One type of electrophotographic image-forming device known in the art is a laser printer having a process cartridge detachably mounted in the body thereof. The process cartridge has a drum cartridge provided with a photosensitive drum for carrying an image thereon, and a developing cartridge that is detachably mounted on the drum cartridge. With this configuration, the developing cartridge and the drum cartridge can be replaced individually when necessary, which from a cost perspective is more advantageous than replacing the cartridges as a unit.
The developing cartridge includes a toner-accommodating chamber that holds toner, and a developing chamber that communicates with the toner-accommodating chamber via a toner supply opening. An agitator provided in the toner-accommodating chamber expels toner from the toner-accommodating chamber into the developing chamber via the toner supply opening. A supply roller, developing roller, and the like are also provided in the developing chamber. The supply roller rotates to supply toner in the developing chamber onto the developing roller. The developing roller then supplies the toner onto the photosensitive drum in order to form a toner image thereon.
The toner image formed on the photosensitive drum is subsequently transferred onto a sheet of paper conveyed through the laser printer, and a fixing unit provided in the body of the laser printer fixes the toner image to the paper, thereby completing the image-forming operation.
There are also various types of developing cartridges that accommodate different quantities of toner. More specifically, there are one type of developing cartridge, in which a maximum amount of toner is accommodated, and another type of developing cartridge, in which a smaller amount of toner is accommodated.